bioindicator

noun

bi‧o‧in‧di‧ca‧tor [countable]technical

a small number of animals, plants, insects etc that are typical of all the animals, plants etc normally found in a particular area, which scientists study in order to get information about the whole area:

This insect-bacteria bioindicator is a reliable tool for assessing environmental damage to the country's wetlands.

Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.